The present invention relates to a cylinder liner insert cast in casting metal when casting a cylinder block for an internal combustion engine to bond the cylinder liner to the cylinder block and form a cylinder bore, a cylinder block formed with such a cylinder liner, and a method for manufacturing a cylinder liner.
There is a type of an internal combustion engine having cylinder liners arranged in a cylinder block. For such an engine, there has been a proposal for a technique for decreasing the temperature difference between the upper and lower portions of a cylinder bore wall during operation of the engine to prevent the fuel efficiency from being lowered and the roundness of the cylinder bores from being decreased due to exhaust gas loss and mechanical loss (refer to, for example, Japanese Laid-Open Patent Publication No. 2001-200751). The technique of Japanese Laid-Open Patent Publication No. 2001-200751 coats an insulative material on the lower portion on the outer wall of each cylinder liner. This adjusts the cooling speed of coolant, which is in contact with the outer wall of the cylinder liner, and decreases the temperature difference between the upper and lower portions of the cylinder bore wall.
However, in Japanese Laid-Open Patent Publication No. 2001-200751, most of the outer surface of the cylinder liner is in contact with the coolant, and only a small portion of the outer surface is in contact with the cylinder block. Accordingly, the cylinder block does not sufficiently support the cylinder liner. It is thus difficult to keep the roundness of the cylinder bore in a satisfactory state.
To sufficiently support the cylinder liner with the cylinder block and keep the roundness of the cylinder bore in a satisfactory state, the outer surface of the cylinder liner may be insert cast in the cylinder block. This bonds the cylinder liner to the cylinder block.
When insert casting the cylinder liner described in Japanese Laid-Open Patent Publication No. 2001-200751 in a cylinder block, the insulative material coating the lower portion of the cylinder liner is made of ceramics. Thus, the bonding between the cylinder liner and the metal forming the cylinder block has a tendency to become insufficient. Therefore, especially, the lower portion of the cylinder liner cannot be sufficiently supported by the cylinder block. This may affect the roundness of the cylinder block.
In this manner, with the cylinder liner described in Japanese Laid-Open Patent Publication No. 2001-200751 that controls the difference in thermal conductivity between the upper and lower portions of the cylinder liner, the roundness of the cylinder bore cannot be sufficiently maintained.